[GitHub] [airflow] kaxil commented on a change in pull request #6175: [AIRFLOW-5545] Fixes recursion in DAG cycle testing

[GitBox <gi...@apache.org>]

kaxil commented on a change in pull request #6175:
URL: https://github.com/apache/airflow/pull/6175#discussion_r496796972



##########
File path: airflow/utils/dag_cycle_tester.py
##########
@@ -32,28 +32,34 @@ def test_cycle(dag):
     Check to see if there are any cycles in the DAG. Returns False if no cycle found,
     otherwise raises exception.
     """
-    def _test_cycle_helper(visit_map: Dict[str, int], task_id: str) -> None:
-        """
-        Checks if a cycle exists from the input task using DFS traversal
-        """
-        if visit_map[task_id] == CYCLE_DONE:
-            return
-
-        visit_map[task_id] = CYCLE_IN_PROGRESS
-
-        task = dag.task_dict[task_id]
-        for descendant_id in task.get_direct_relative_ids():
-            if visit_map[descendant_id] == CYCLE_IN_PROGRESS:
-                msg = "Cycle detected in DAG. Faulty task: {0} to {1}".format(task_id, descendant_id)
-                raise AirflowDagCycleException(msg)
-            else:
-                _test_cycle_helper(visit_map, descendant_id)
-
-        visit_map[task_id] = CYCLE_DONE
-
     # default of int is 0 which corresponds to CYCLE_NEW
     dag_visit_map: Dict[str, int] = defaultdict(int)
     for dag_task_id in dag.task_dict.keys():
         if dag_visit_map[dag_task_id] == CYCLE_NEW:
-            _test_cycle_helper(dag_visit_map, dag_task_id)
+            _test_cycle_helper(dag_visit_map, dag_task_id, dag.task_dict)
     return False
+
+
+def _test_cycle_helper(visit_map, task_id, task_dict):
+    """
+    Checks if a cycle exists from the input task using DFS traversal
+    """
+    path, visited = deque([task_id]), []

Review comment:
       ```suggestion
       tasks, visited = deque([task_id]), []
   ```




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